Modeling and calibrating a three-port time-domain reflectometry system

Abstract

A three-port TDR front end comprises numerous components. An exemplary three-port TDR front end is a DSL modem. Information-bearing TDR signals are distorted as they pass through these components. With a perfect model of the response of its front-end, a TDR system usually can compensate for the effects of its front-end. In reality, however, the electrical characteristics of each component vary from design-to-design, board-to-board, and slowly over time. The result is imperfect knowledge about the true response of the front-end, errors in the model of the front-end, and degraded TDR performance. At least for this reason it is important to precisely calibrate the response of the TDR front-end through the use of a TDR modeling system.

1 . A method of predicting the response of a linear, time-invariant system comprising:
 connecting a device to a third port;   transmitting a waveform from a first port;   receiving an echo response of the waveform at a second port;   determining at least three system responses when the third port is connected to each of at least three different devices, wherein the electrical characteristics of the at least three devices are known;   determining three parameters that characterize a front-end; and   using the three parameters to predict the system response when the front-end is connected to any device.   
     
     
         2 .- 36 . (canceled)